CSSで線の太さを太くしたい

実現したいこと

線の太さを太くしたい（写真の薄黄色箇所）

前提

写真の薄黄色箇所の線を太くしたいです。
その為、「border-bottom」プロパティを用いて太くさせようとしましたが、全く変化がなく困っております。

どこのクラスに対して、どのプロパティを設定すると該当箇所を太くするように出来るのでしょうか。

該当のソースコード

CSS

1/* コース案内 2------------------------------------------ */3 4.guidance .container {5 padding-top: 4.35rem;6}7 8@media (min-width: 768px) {9 .guidance .container {10 padding: 5.65rem 0;11 }12}13 14.guidance .guidance-title {15 position: relative;16 top: 0.5rem;17 margin-bottom: 2rem;18 text-align: center;19}20 21@media (min-width: 768px) {22 .guidance .guidance-title {23 margin-bottom: 2.5rem;24 font-size: 2.25rem;25 }26}27 28/* コース案内タイトル下の擬似要素 */29.guidance-title::after {30 content: "";31 display: block;32 width: 1.5rem;33 height: 0.125rem;34 background-color: #0079f1;35 position: absolute;36 bottom: -0.6rem;37 left: 10.6rem;38}39 40@media (min-width: 768px) {41 .guidance-title::after {42 left: 32.7rem;43 bottom: -0.8rem;44 width: 2.25rem;45 }46}47 48 49 50/* タブ */51.st-theme-basic {52 border: none;53 padding: 0 0.1rem 0.8rem;54}55 56/* タブナビゲーション */57.tab.st>.nav {58 position: relative;59 top: 1.16rem;60 height: 4rem;61 column-gap: 0.5rem;62 flex-direction: row !important;63}64 65@media (min-width: 768px) {66 .tab.st>.nav {67 top: 1.4rem;68 height: 5.2rem;69 column-gap: 1.6rem;70 }71}72 73.tab.st-theme-basic>.nav {74 box-shadow: none;75}76 77.tab.st-theme-basic>.nav .nav-link {78 padding-top: 1.15rem;79 padding-bottom: 1.25rem;80 line-height: 1.4;81 background-color: #d8d8d8;82 color: #000;83 border-radius: 0.5rem 0.5rem 0 0;84 font-size: 1.125rem;85}86 87@media (min-width: 768px) {88 .tab.st-theme-basic>.nav .nav-link {89 padding-top: 1.45rem;90 padding-bottom: 1.5rem;91 font-size: 1.625rem;92 line-height: 1.6rem;93 }94}95 96/* アクティブ状態 */97.tab.st-theme-basic>.nav .nav-link.active {98 color: #fff !important;99 background-color: #f2a118;100}101 102.tab.st-theme-basic>.nav .nav-link.active::after {103 background-color: unset !important;104}105 106/* タブコンテンツ */107.tab-content {108 text-align: center;109 background-color: #ffedcc;110 border-radius: 0 0 1.25rem 1.25rem;111 padding: 1rem 1rem 1rem 1rem;112 top: 1.1rem;113}114 115.tab.st-theme-basic>.tab-content>.tab-pane {116 flex-direction: column;117 background-color: #fff;118 border-radius: 0.5rem;119 padding-bottom: 4.6rem;120}121 122@media (min-width: 768px) {123 .tab.st-theme-basic>.tab-content>.tab-pane {124 justify-content: space-between;125 flex-direction: row;126 padding-bottom: 2rem;127 }128}129 130/*----------1タブ目----------*/131/*---写真1枚目---*/132.baby-course img {133 position: relative;134 top: 0.7rem;135 width: 92%;136}137 138@media (min-width: 768px) {139 .baby-course img {140 top: 1.3rem;141 left: 1.2rem;142 width: 100%;143 }144}145 146/*コース名*/147.baby-course .guidance-tab-content-title-top {148 position: relative;149 top: 0.7rem;150 font-size: 1.25rem;151}152 153@media (min-width: 768px) {154 .baby-course .guidance-tab-content-title-top {155 top: 1.2rem;156 left: 1.2rem;157 font-size: 1.5rem;158 }159}160 161/*対象年齢*/162.baby-course .guidance-tab-content-title-bottom {163 position: relative;164 top: 0.4rem;165}166 167@media (min-width: 768px) {168 .baby-course .guidance-tab-content-title-bottom {169 top: 0.6rem;170 left: 1.2rem;171 font-size: 1.125rem;172 }173}174 175/*---写真2枚目---*/176.junior-course img {177 position: relative;178 top: 2.2rem;179 width: 92%;180}181 182@media (min-width: 768px) {183 .junior-course img {184 top: 1.1rem;185 width: 100%;186 }187}188 189/*コース名*/190.junior-course .guidance-tab-content-title-top {191 font-size: 1.25rem;192 position: relative;193 top: 2.2rem;194}195 196@media (min-width: 768px) {197 .junior-course .guidance-tab-content-title-top {198 top: 1.3rem;199 left: 0.1rem;200 font-size: 1.5rem;201 }202}203 204/*対象年齢*/205.junior-course .guidance-tab-content-title-bottom {206 position: relative;207 top: 1.9rem;208}209 210@media (min-width: 768px) {211 .junior-course .guidance-tab-content-title-bottom {212 top: 0.6rem;213 left: 0.1rem;214 font-size: 1.125rem;215 }216}217 218/*---写真3枚目---*/219.senior-course img {220 position: relative;221 top: 3.8rem;222 width: 92%;223}224 225@media (min-width: 768px) {226 .senior-course img {227 top: 1.3rem;228 left: -0.9rem;229 width: 100%;230 }231}232 233/*コース名*/234.senior-course .guidance-tab-content-title-top {235 font-size: 1.25rem;236 position: relative;237 top: 3.7rem;238}239 240@media (min-width: 768px) {241 .senior-course .guidance-tab-content-title-top {242 top: 1.25rem;243 left: -1rem;244 font-size: 1.5rem;245 }246}247 248/*対象年齢*/249.senior-course .guidance-tab-content-title-bottom {250 position: relative;251 top: 3.5rem;252}253 254@media (min-width: 768px) {255 .senior-course .guidance-tab-content-title-bottom {256 top: 0.6rem;257 left: -1rem;258 font-size: 1.125rem;259 }260}261 262/*----------2タブ目----------*/263/*---写真1枚目---*/264.lowergrade-course img {265 position: relative;266 top: 0.7rem;267 width: 92%;268}269 270@media (min-width: 768px) {271 .lowergrade-course img {272 top: 1.3rem;273 left: 1.2rem;274 width: 100%;275 }276}277 278/*コース名*/279.lowergrade-course .guidance-tab-content-title-top {280 position: relative;281 top: 0.7rem;282 font-size: 1.25rem;283}284 285@media (min-width: 768px) {286 .lowergrade-course .guidance-tab-content-title-top {287 top: 1.2rem;288 left: 1.2rem;289 font-size: 1.5rem;290 }291}292 293/*対象年齢*/294.lowergrade-course .guidance-tab-content-title-bottom {295 position: relative;296 top: 0.4rem;297}298 299@media (min-width: 768px) {300 .lowergrade-course .guidance-tab-content-title-bottom {301 top: 0.6rem;302 left: 1.2rem;303 font-size: 1.125rem;304 }305}306 307/*---写真2枚目---*/308.upper-grade-course img {309 position: relative;310 top: 2.2rem;311 width: 92%;312}313 314@media (min-width: 768px) {315 .upper-grade-course img {316 top: 1.1rem;317 width: 100%;318 }319}320 321/*コース名*/322.upper-grade-course .guidance-tab-content-title-top {323 font-size: 1.25rem;324 position: relative;325 top: 2.2rem;326}327 328@media (min-width: 768px) {329 .upper-grade-course .guidance-tab-content-title-top {330 top: 1.3rem;331 left: 0.1rem;332 font-size: 1.5rem;333 }334}335 336/*対象年齢*/337.upper-grade-course .guidance-tab-content-title-bottom {338 position: relative;339 top: 1.9rem;340}341 342@media (min-width: 768px) {343 .upper-grade-course .guidance-tab-content-title-bottom {344 top: 0.6rem;345 left: 0.1rem;346 font-size: 1.125rem;347 }348}349 350/*---写真3枚目---*/351.examinationbasic-course img {352 position: relative;353 top: 3.8rem;354 width: 92%;355}356 357@media (min-width: 768px) {358 .examinationbasic-course img {359 top: 1.3rem;360 left: -1rem;361 width: 100%;362 }363}364 365/*コース名*/366.examinationbasic-course .guidance-tab-content-title-top {367 font-size: 1.25rem;368 position: relative;369 top: 3.7rem;370}371 372@media (min-width: 768px) {373 .examinationbasic-course .guidance-tab-content-title-top {374 top: 1.25rem;375 left: -1rem;376 font-size: 1.5rem;377 }378}379 380/*対象年齢*/381.examinationbasic-course .guidance-tab-content-title-bottom {382 position: relative;383 top: 3.5rem;384}385 386@media (min-width: 768px) {387 .examinationbasic-course .guidance-tab-content-title-bottom {388 top: 0.8rem;389 left: -1rem;390 font-size: 1.125rem;391 }392}393 394/*----------3タブ目----------*/395/*---写真1枚目---*/396.juniorhighschoolbasic-course img {397 position: relative;398 top: 0.7rem;399 width: 92%;400}401 402@media (min-width: 768px) {403 .juniorhighschoolbasic-course img {404 top: 1.2rem;405 left: 1.2rem;406 width: 100%;407 }408}409 410/*コース名*/411.juniorhighschoolbasic-course .guidance-tab-content-title-top {412 position: relative;413 top: 0.7rem;414 font-size: 1.25rem;415}416 417@media (min-width: 768px) {418 .juniorhighschoolbasic-course .guidance-tab-content-title-top {419 top: 1.3rem;420 left: 1.1rem;421 font-size: 1.5rem;422 }423}424 425/*対象年齢*/426.juniorhighschoolbasic-course .guidance-tab-content-title-bottom {427 position: relative;428 top: 0.4rem;429}430 431@media (min-width: 768px) {432 .juniorhighschoolbasic-course .guidance-tab-content-title-bottom {433 top: 0.7rem;434 left: 1.1rem;435 font-size: 1.125rem;436 }437}438 439/*---写真2枚目---*/440.juniorhighschoolapplied-course img {441 position: relative;442 top: 2.2rem;443 width: 92%;444}445 446@media (min-width: 768px) {447 .juniorhighschoolapplied-course img {448 top: 1.1rem;449 width: 100%;450 }451}452 453/*コース名*/454.juniorhighschoolapplied-course .guidance-tab-content-title-top {455 font-size: 1.25rem;456 position: relative;457 top: 2.2rem;458}459 460@media (min-width: 768px) {461 .juniorhighschoolapplied-course .guidance-tab-content-title-top {462 top: 1.3rem;463 font-size: 1.5rem;464 }465}466 467/*対象年齢*/468.juniorhighschoolapplied-course .guidance-tab-content-title-bottom {469 position: relative;470 top: 1.9rem;471}472 473@media (min-width: 768px) {474 .juniorhighschoolapplied-course .guidance-tab-content-title-bottom {475 top: 0.8rem;476 font-size: 1.125rem;477 }478}479 480/*---写真3枚目---*/481.advancedcertification-course img {482 position: relative;483 top: 3.8rem;484 width: 92%;485}486 487@media (min-width: 768px) {488 .advancedcertification-course img {489 top: 1.2rem;490 left: -1.1rem;491 width: 100%;492 }493}494 495/*コース名*/496.advancedcertification-course .guidance-tab-content-title-top {497 font-size: 1.25rem;498 position: relative;499 top: 3.7rem;500}501 502@media (min-width: 768px) {503 .advancedcertification-course .guidance-tab-content-title-top {504 top: 1.3rem;505 left: -1.1rem;506 font-size: 1.5rem;507 }508}509 510/*対象年齢*/511.advancedcertification-course .guidance-tab-content-title-bottom {512 position: relative;513 top: 3.5rem;514}515 516@media (min-width: 768px) {517 .advancedcertification-course .guidance-tab-content-title-bottom {518 top: 0.8rem;519 left: -1.1rem;520 font-size: 1.125rem;521 }522}523