grid-template

Возможные записи:

/* Keyword value */
grid-template: none;

/* grid-template-rows / grid-template-columns values */
grid-template: 100px 1fr / 50px 1fr;
grid-template: auto 1fr / auto 1fr auto;
grid-template: [linename] 100px / [columnname1] 30% [columnname2] 70%;
grid-template: fit-content(100px) / fit-content(40%);

/* grid-template-areas grid-template-rows / grid-template-column values */
grid-template: "a a a"
               "b b b";
grid-template: "a a a" 20%
               "b b b" auto;
grid-template: [header-top] "a a a"     [header-bottom]
                 [main-top] "b b b" 1fr [main-bottom]
                            / auto 1fr auto;

/* Global values */
grid-template: inherit;
grid-template: initial;
grid-template: unset;

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Более подробно на MDN